Portable stroboscope having pistollike frame and indicator lock



9 Sheets-Sheet l G. SCHWEISTHAL FRAME AND INDICATOR LOCK PORTABLE STROBOSCOPE HAVING PISTOLA-LIKE April 26, 1949.

Filed Nov. 26, 1943 April 26, 1949. F. G. scHwElsTl-IAL PORTABLE STROBOSCOPE HAVING' PISTOL-LIKE FRAME AND INDICATOR LOCK 9 Sheets-Sheet 2 Filed NOV. 26, 1943 Y. mw

WN Nm 2,468,690 -LIKE April '26, 1949. F. G. scHwElsTHAL PORTABLE STROBOSCOPE HAVING PISTOL FRAME AND INDICATOR LOCK 9 Sheets-Sheet 3 Filed Nov. 26, 1945l Apnl 26, 1949. F. G, scHwl-:lsTHAL 2,468,690

' PORTABLE STROBOSCOPE HAVING PISTOL-LIKE FRAME AND INDICATOR LOCK Filed Nov. 26, 1943 9 Sheets-Sheet 4 April 26, 1949. F. G. scHwElsTHAl. 2,468,690

PORTABLE STROBOSCOPE HAVING PISTOL-LIKE FRAME AND INDICATOR LOCK 9 Sheets-Sheet 5 Filed Nov. 26, 1945 April 26, 1949.

F. G. SCHWEISTHAL PORTABLE STROBOSCOPE HAVING PISTOL-LIKE FRAME AND INDICATOR LOCK Filed Nov. 26, 1945 l-hil n-l 9 Sheets-Sheet 6 April 26, 1949 F. G. scHwl-:lsTHAL 2,468,690

PORTABLE STROBOSCOPE HAVING PISTOL-LIKE FRAME AND INDICATOR LOCK Filed NOV. 26, 1943 9 Sheets-Sheet '7 April 26, 1949. F. G. scHwElsTl-IAL 2,468,690

PORTABLE STROBOSCOPE HAVING PISTOL-LIKE April 26, 1949. F. G. scHwElsTHAl.

PORTABLE STROBOSCOPE HAVING PISTOL-LIKE FRAME AND INDICATOR LOCK 9 Sheets-Sheet 9 Filed Nov. 26, 1943 Patented Apr. 26, 1949 ES PATENT -OFFICE PORTABLE STRQBQSCOBE HAVlNGJPISTQL- IIIKETRAME `AND INDICATOR-LOCK Frederick G. chweisthal, Skokie, Ill., assignorato .nstewart-Warner orporaiion, Qhiagm :Ille e ecornorationgof .Virginia VApplication November 26, 1943,Serial-'No.r51L8S5 (CLI-,$37.14)

I livry invention .relates to eportabls. sirobnsopes vandi-s-more:aparticuiazrly .concerned with; a eportable stroboscope @especially adapted to indicate the =spee`d-of a shaftorecitli er1 moving Apart.

An object of myeinvention fisi: to-.fprovidea port- `able ystrobosoope :which :may be `connected to .a Abattery -lcarriedbyfthe user and vwhichv can :readiiy be `moved `-from fplace :to spiace -zto indicate the Another object -.-.of ,invention y:is @to provide Vla, portable:.stroboscopeihaving new and improved vspeed indicatingemeans.

Anotherobject:of-emysinvention iisv to -provide a portable Ystroboseipe .having Inew rand improved vspeed control mechanism Another Aobjectrif amyinvention isstov provide .a

:portable stroboseope `fhaving new :and .improved switch fmechanism.

:Anothery obj ect-of my invention i. is '.to provide a `portable Vstroboseope-having new and improved .viewing-mechanism.

Another object- -of my '.-inventions is Ito provide -a A'new Aand rimprovediportablesstroboscope whioh is vlight 1in -vweight,.;ioompact, inexpensive `:to manufacture, Jeasy gto seperate, fandcapable of .giving long :and itroublefxteeervice.

IAnotherrolojeetofvmyfinvention i is to provide a f portable' stro-boscope -whichmayabeureadily radaptedfto indicate;thepeedofmachinqparts operat- 'ingai; widelyfdiierent-speeda Other-objeotsof'l my invention-will beeome ap :parent as' thedeseriptionproceeds.

`InA theI drawings: #Figyl'is a longitudinalgseetional View yof a pre -Fig.; 2 is-anf-endxviewitakenfrom the left of to showe'details--of viconstruction:

Fig fiisfan 'and vieWjlook-irig towardtliejleft in' Fig. 11;

Fie. l is :an .enlargedLlogeitudinal .sectional view of jtlielefthaind :end59f ',1;

`rFig.-6 is a'transverse section taken onine line 6-6 Ofligf. but` slioiviagrarts of' themaindial .broken `away ..150 dilQSe 112116 @Structure A therebeneath;

Figa isfani irregularfiftransverse sectonitaken .onthelinej '10i A5;

IFig. 8 is .an irregular, partial, ltransvarse .sec-

8&5; F-gwas anzirfiillamiiiarisverse; .section teken Fig. `210 isanerllarged,l sectional viewroithe lian- -dleeandassociated ,mevchanism;

Fig. ,'11 y,is a partial ,setpn taken on the line l l-i l of Fig. 10 showing the switch rneohanism;

Fig. .12 is a transversesectionthrough-the-11andletaken onithe, line .Igzfilz oJEig. 10

' 1/Fig. 21-3 is a wiring diagram;

Figs- 11., 15 .and V1.6 .are views showing diiererli -typesof soanningdiscs Fig lz'fisa sectional View taken onthe'line -I-1 lil lof Fig. Sshowing a detailvof `tlrrespeed governor;

Figfljis 4a:transverseseetiori takenon the line ieg-le Ifer-rig. 1,;

:F.ig. 19 `is a view-:showing the governing mech- ,anism 4-in expanded position;

Fig 20 is Aan irregular. transverse section ltaken oni-the line5 20- 20 of Fig. 1;

v and provided with -a pistol-like gripf'l A.whereby the stroboscope may be readily `carried. in one vriend-0f :theeuser andpointed toward .theobiect `Whosespeed is tdbedetermined. The two-piece gri-p` is s secu-red to the housing i 3 0 ibyy boltsg33 Y(Figs.

;l 0;and 20). :An electric motor; 34 :is mounted in the .housing .-310 tand ,drives .a shaft :136 4.which rotates a scanning diss-,38- -zThis scanning disc lisfremovably clamped between .the shoulder@ anda `Washer.112-

shoulderpiiis providedfby acollar `4l! which isLattaehedytofthe straft 36 for .rotation therewithby-meansof asorewgli. The .washerllz isheld againstone side ofztheldiscz by a nut 48 removably threaded to thereducedextension of.y the collar A4.

prises four sets-of `circular.viewing bands, `each ban-d flieirigl composedA of alternate clearl segments or windowsv of larcuate conformation i andl opaque segments likewise oflarcuate conformation. In

Fig; 14 ythe inrier-bandis` illustrated .as .having a single LvWindow.indicated rby the.letter C and a single opaque-segment indicatedfloythe letter vB. The.adjacent .band vcomprises-a pair of Windows -.and a pairl of alternating opaquel segments,

Whereasathe third..band-has vtlfiree-Windows and three opaque -segrr1ex1ts,arid the fou-rth'or outer band 4has four Windowsand Yfour opaqueY segments` The disc 38 may -be made of any sul` Table 3 materials and in any suitable manner but is preferably formed of transparent plastic or other suitable material and painted black to provide the opaque segments.

In Fig. 15 I have shown an alternative scanning disc 38 likewise having four viewing bands but wherein the innermost band has live windows and ve opaque segments, the next band six windows and six opaque segments, the next seven Windows and seven opaque segments, and the outermost band eight windows and eight opaque segments. In Fig. 16, a third scanning disc 38" has an innermost viewing band containing nine windows and nine opaque segments, an adjacent band containing ten windows and ten opaque segments, a third band containing `eleven windows and eleven opaque segments, and a fourth or outer band containing twelve windows and twelve opaque segments. It is to be understood that either the disc 38 or the disc 38" may be substituted for the disc 38 to adapt the stroboscope for use with machine parts operating in widely different speed ranges.

The right-hand end of the tubular housing 30 is provided with a radially extending ange 52 having an oblong opening 54 formed therein and provided with a strip 56 of transparent plastic or other material covering this opening and secured to the flange 52 by screws 58 or in any other suitable manner. A door or cover 60 has one edge pivotally attached to the ange 52 by a hinge 62, and the opposite edge of the cover 60 is provided with a suitable latch 64 for securing the cover in closed position. As best shown in Fig. 3, this latch may be a thumb screw or any other suitable device for holding the cover in closed position while the stroboscope is in use, but which permits the cover to be readily swung to open position to change viewing discs to adapt the stroboscope for use with parts operating at a speed outside of the speed range of the particular disc theretofore in use.' -The cover 60 is provided with an opening 66 which registers with the opening 54 when the cover is in closed position, and a strip 68 of suitable transparent material is attached to the cover and closes the opening B6.

A centrifugal governor 'is mounted on the shaft 36 for rotation therewith and comprises three resilient strips each having one end secured to the fixed collar 44 by means of a screw 12. The other end of each strip 10 is secured by a screw 14 to a second collar 16 which is slidable lengthwise of the shaft 36 and carries a brake disc 18. A weight 80 is attached to the center of each strip 10 so that as the shaft 36 revolves, centrifugal force tends to move these weights ing suitably secured to the tubular housing 30 and containing a resistance 94 in series with the motor field coil 96 (Fig. 13). A slider 68 is carried by the shaft 84 and moves over the resistance 04 to vary the supply of current to the motor eld coil. The rheostat shaft 84;is.rotated by a knob |06 secured to the outer end of the shaft 84 by a screw |02 and serves simultaneously to vary the motor speed and to adjust the eccentric governor brake member 82 to condition the govv ernor to maintain the desired speed of the shaftA 36.

The speed indicating mechanism includes a collar |04 secured by a screw |06 to the left-hand and the washer ||2 to adjust the position of the magnet axially of the collar |04. The magnet is held in place by a ring ,|`|6 secured to the collar |04 by a screw H8. The magnet |08 rotates in the right-hand end of Aa tubular field piece |20 adjustably threaded lin a supporting ring |22. The field piece |20 is-composed of magnetic material, whereas the collar |04 and ring I|6 are preferably formed of non-magnetic material.

The ring |22 is attached by screws |24 to the ange of a cup |26 whose base'is attached in any suitable mannerv to the adjacent end of the motor 84. The annular eld piece |20 may be adjusted relative to the magnet |08 by rotating a shaft |28 having teeth |30 engaging complementary teeth |32 integral with the left-hand end of the field piece |20. The shaft |28 has a hollow right-hand endv surrounding 'a guide bearing |34 riveted to the ring |22 and is rotatably mounted in supportfrom the position shown in Figs. 1 and 18 to the is clamped between a pair of metal washers 88,l

and the assembly comprising these washers and the brake member is clamped against a shoulder 00 of the rheostat shaft by means of a nut 92 screwed to the threaded upper end of this shaft (Fig. 3).

The rheostat 86 comprises a sheet metal casing partitions |36 and |38 hereinafter described in greater detail.' The left-hand end of the shaft |28 is provided with a screwdriver slot |40 to permit rotation of this shaft and adjustment of field piece |20. Shaft |28 is held in adjusted position by spring wire |4| having one end soldered to partition |38, as indicated at |43 in Fig. 6. The other end of wire 14| has a loop |45 which may be engaged yby a hook to remove the wire from slot |40 during adjustment of shaft |28 and thereafter to replace the wire in this slot.

Rotation of the magnet |08 tends to rotate a non-magnetic speed cup |42 mounted on an indicator shaft |44. vOne end of this shaft |44 is journalled in a jeweled bearing |46 carried by a fixed, non-magnetic cup |48 attached by means of rivets |50 and spacing sleeve |52 to the base of the cup |26. The indicator shaft |44 is supported in a second jeweledbearing |54 carried by the plate |38. The extreme left-hand end of the shaft I 44 carries a pointer |56 movable over a graduated dial |58vvisible through the glass window |60 of a cover |62 removably attachedv to the left-hand end of the tubular housing 30 by means of screws |64.

Partition |36 is secured to the rim of cup |26 by short posts |65 and screws |61. Longer posts |66 arealso mountedv on the rim of the cup |26 and support partition |38 and dial |58. rPartition |38 is clamped by nuts |68 against shoulders provided by posts |66, and dial |58' is secured to the ends of -theseposts by screws |10 and washers |12. Dial |58 is provided with an opening |14 opposite the end of shaft |'28`to provide access to this shaft and spring wire |4| when the cover .ascenso |62 -is :removed so that the shaft may be rotated to'adjust thefleld piece |20 relative to the magnet |03.

A vcollar |16 is attached .to the indicator shaft |44 :for rotation therewith and has teeth |18 en- .gaging the teeth of ra gear '|80 mounted `on a secondary indicator shaft |82. This secondary shaft is mounted 4in Jeweled Ybearings 1M and |86. The bearing .ll-B4 is mounted'ina bracket |88 attached to cup |26, and the bearing 'f8.6 :is mounted in anoset portion '|911 of vpartition 138.' Shaft |82 has attached thereto an auxiliary indi -cator disc |92 having indicia .suitably .marked thereon and intended to be moved into registry with-an arcuate opening v| 94 in the 'dial 15.8. The indicator shafts |44 and 1.182 are urgedtowardzzero position by a spiral spring |26 :having one .end vattached to a collar |88 "mounted "onrshait 1.82, Aand a second end attached toa xed stop 2.00 (Fig. 7) attached to the partition 1:38. lhestop 286 has a bent-over end .202 adapted to vbe engaged by the bent-.over portion A2.04 of a .strip .266 movable with gear |86 and-shaft |182.

.In use, .the stroboscope is pointed toward the shaft or other moving object whosespeed is to be indicated, and the operator looks through the windows 54 and 65 while he ladjusts the manual control button |00 of the rheostat to vary the motor speed and bring the window or windows oi one band of the scanning disc into synchronism with the shaft or other moving part. `Rotation -of the permanent magnet |08 creates .afdrag on speed cup |42 proportional to the vspeed of the shaft 36 on which the scanningdisc is mounted. Rotation of speed cup |=42 under the inuence oi' this drag is resisted by spiral spring |96, libut `the speed cup and shafts |44 and |82 driven therefrom rotate to cause pointer 1:56 .and indicator disc |92 to assume positions accurately reflecting `the speed of shaft 36 .and of the scanning disc carried thereby. When a particular band of the scanning disc is in'synchronism `with the rotating part whose speed is being checked, .the operator may vglance at pointer |56 and indicating disc '|192 to see the reading thereof.

I have found it more convenient, however, to provide means for locking this pointer `and indi eating disc in xed position as soon asa particular band of the scanning #disc is :broughtintoxsynchronisrn with the rotating ,part beingmeasureii, as this ygives the `operator more time to view and read the indicating means accurately. Referring to Fig. 5, it will be noted that 44the collar |515 attached to the speed cup shaft |41! vcarries a brake drum 20.3 adapted to be engaged byarbrake shoe 2 of felt-.or other suitable material. .As best shown in Fig. 8, the brake shoe 21|!! is mounted on a resilient arm 2|2 attached at `2|4 to the partition |36. A spring 2|6 is interposed between the arm 2| 2 anda fixed vsupport 25|.8 provided fby partition |36 and urges the .brake 'shoe 2H) toward the brake drumi2 |18. The-brakeshoe is'withdrawn .fromengagement with the brake drum by an electromagnet 220 which attracts an armature `222 attached .to the arm 2|2.

I have provided latch means which normailly holds the brake shoe '2|0 in retracted position. This latch meanscomprises a second resilient arm 22@ mounted on the -partition |36 as indicated at 226. The arm 224 has a slot 22 Badaptedto receive the tongue 230 formed bythe extreme let end `or freeendof the arm 2|2. When the free end I'of the brake lcarrying arm 2|2 is retracted :by electromagnet 220, the tongue 230 of this arm moves .opposite the slot 22B `in` arm 2-24 whereupon .this

latter :arm 'is moved to the :right by :a spring 232 lcuniined between this arm and a xed support 23d yprovidedbythe partition |36. .Engagement oi the tongue 23|) in the slot 228 serves to hold the brake shoe 2|!) in retracted or inoperative posif tion until the latch is 'released by a second electromagnet 236 mounted on the partition |36 and operative to attract an armature 2.3.6 :attached t0 the free end of the .latch arm 224. When the upper end of latch arm 224 is drawn to the left by magnet 236, tongue 23|! passes out of slot 226 and spring 2|6 applies the brake shoe 2li).

.Application and release yof the indicator brake are controlled by switch mechanism operated by a trigger 240 associated with the piston grip 32. 'This switch mechanism is kbest 'shown in Rigs. 10, `l1 and 12, and ycomprises a slide or actuator 24.2 to Vwhich the trigger 240 is attached by ascrew 244. The actuator 242 has a slot 246 receivinga guiding and retaining pin 248 and -a shaft 25B .both carried by -a support 252 attached to the grip .32 by screws 254. The actuator .242 and trigger 246 are urged toward the right by a spring 256 confined between the left-hand end of the actuator and an opposed end of the support 252.

A ratchet wheel v258 is aixed to the shaft 256 and is given a step by step rotation by a resilient pawl 266 carried .by the actuator 242. Retrograde ymovement of the ratchet wheel 2,53 and lshaft Y250 is prevented by a resilient pawl 2.62 attached to the support 252. A switch operating wheel 264 is also afxed tothe shaft 25!) and serves to control a pair of switches indicated generally 'by reference characters A and B which control electromagnets 236 and 22.6 respectively.

As clearly shown in Fig. 11, the switch A comprises switch arms 266 and 268 suitably mounted `in a bracket 21.6 of the support 252 and properly Yinsulated therefrom. The switch B likewise comprises `switch arms 212 and 211i also supported from the bracket 216 and insulated therefrom. Switch arm 2368 is positioned just to the left of the switch operating Wheel 264 and is adapted to be engaged by lateral projections 216 formed on one side of this wheel. Such engagement moves the upper end of switch arm 266 to the left `to bring the contact carried by this end into engagement with the contact carried by the upper end of switch arm 266 with resultant supply of current to the electromagnet 236. This magnet releases a latch which Vresults in application .of the brake shoe 2li) so that the switch A controls lapplication of the indicator brake.

Arm 214 of switch B has its upper end lying just tothe right of actuating wheel 2.64 and is adapted to be engaged by projections 216 extending laterally from the right-hand side of this wheel. Such engagement causes the lContact at the upper end of arm 214 to engage the contact at .the .upper end of the arm 212 and supplies .current to the brake release magnet 22! to withdraw brake shoe 2 6 from engagement with brake -drum 208. Itis thus apparent that switch B controls release of the indicator brake. It is only necessary to energize the magnets 22E) and 236 momentarily in order to control the application .and release of the indicator brake and the projections 216 Aand 218 are so arranged that they engage their respective switches only during the midstroke of the trigger 2116 and actuator 242.

As clearly shown in the drawings, the projections 216 and 213 are arranged alternately about the circumference of the actuator vwheel 264 and .are-so spaced that only yone of these yprojections vengages :a switch for each complete stroke of :the

trigger 240 and actuator 242. This means that when the trigger is first operated, it energizes the latch release magnet 235 to apply the indicator brake. Upon release of pressure on the trigger 24U, retractor spring 256 returns the trigger and actuator to initial position. When it is desired to release the indicator brake, the operator again presses on the trigger 240, whereupon the switch B of the brake release magnet 220 is momentarily closed and the brake shoe is withdrawn to inoperative position and is held in this position by the mechanical latch mechanism. As soon as finger pressure is released, the trigger 24B and actuator 242 are again returnedto extended position by spring 255.

From the foregoing, it will be apparent that the switches for controlling the indicator brake mechanism cannot be maintained in closed position for any appreciable length of time unless the operator deliberately abuses the stroboscope by holding the trigger in intermediate position. This is an important feature of my invention as it protects the electromagnets against overheat ing and the battery against unnecessary drains. In Fig. 13, I have shown a wiring diagram wherein the source of current is indicated as a battery 300 connected by suitable wires and through suitable brushes to the motor armature SH2. This battery is also connected to the motor eld coil 95 by way of the rheostat comprising the resistance 94' and slider S8. The battery 3U@ also furnishes current to the electromagnets 225 and 236 by way of the trigger controlled switches A and B. While I have shown and described my portable stroboscope as being supplied with current from a battery, any other suitable source of current may be utilized in lieu of this battery.

In Figs. 22 and 23, I have shown a modified form of my invention which is identical with that previously described except that the return spring for the indicating mechanism is mounted on the main indicating shaft instead of on the auxiliary shaft. In the embodiment of Figs. 22 and 23, a large spiral return spring 350 has one end attached to a collar 352 on the speed cup shaft IM' and the other end of this spring is wrapped around one of the partition supporting posts 65. Discs 354 and 355 are attached to the collar 352 on opposite sides of the spring 350 and limit lateral movement of this spring. discs rotate with speed cup shaft Mil', frictional resistance created by engagement of these discs with the spring 350 is minimized and has no effect on the reading of the indicating mechanism. I contemplate that my portable stroboscope will be used by an operator who walks about a factory to determine the rotating speed of various shafts or other moving parts of the several machines installed in the factory. For such purposes the operator would carry a case strapped to his back and the flexible electric cord 351 of the portable stroboscope would be provided with a terminal which could be inserted in and removed from a suitable socket provided by the carrying case. This carrying case would preferably contain a suitable battery, such as a 6 Volt D. C. battery, and a selenium rectifier for converting 110 alternating current into 6 volt direct current. A switch would be provided so that the socket would be connected with either the battery or rectifier and the rectifier, of course, would be in circuit with a long, ilexible cord which could be plugged into the lighting system of the factory.

Such an arrangement would have the advantage of permitting the use of alternating current Since these I Whenever this current were readily available. The battery would be lconserved by being used only when a suitable source of alternating current is not available or when the operator is moving rapidly from one machine to another and it is not convenient to plug into an alternating current source.

In some instances it may be desirable to make a prolonged study of a particular machine and in .such instances it is, of course, preferable to utilize the lighting system of the factory as a. source of current. In such prolonged studies it may also be desirable to mount the stroboscope on a suitable support, such as a camera tripod,

r and for this purpose I have provided the base of the handle with a socket 358 which may be readily secured to the usual camera tripod. The carrying case containing the battery and rectier may also serve as av storage receptacle for the additional scanning discs.

It will be understood, however, that the foregoing paragraphs refer only to a few of the numerous uses to which my portable stroboscope may be put. It is not necessary that the stroboscope be operated by a 6 volt direct current motor, as any other type of motor may be used in lieu thereof. The carrying case to which I have reference constitutes only one of several advantageous arrangements for supplying current to the stroboscope and any other suitable arrangement may be provided.

When the operator wishes to determine the speed of a shaft, he points the portable stroboscope at the shaft just as he would a pistol, and sights through the windows aligned on opposite sides of the scanning disc. If none of the four bands of the scanning disc happens to be in synchronism with the shaft at which the stroboscope is pointed, the operator adjusts the knob |00 of the rheostat in an effort to bring one of these scanning bands into synchronism with the shaft. If no band of the particular scanning disc in the stroboscope can be brought into synchronism with the shaft, the operator stops the stroboscope and replaces the particular scanning disc therein with another scanning disc, and repeats the operation.

As soon as one band of the scanning disc is brought into synchronism with the shaft, i. e., as soon as the clear segments of this band move past the sighting windows with such speed as to make the shaft appear to stand still, the operator presses on the trigger 240 to set the indicator brake. The operator can then lower the stroboscope to bring the indicators into a position where they may be more easily read. After he has read the indicators he returns the stroboscope to sighting position and again sights on the shaft to ascertain that the particular band of the scanning disc is still in synchronism with the shaft, and that the indicator reading therefore correctly reflects the speed of this shaft.

If this check shows that the indicator reading is correct, the operator presses the trigger to release the indicator brake and passes on to the next machine whose speed is to be determined. If, however, the check sight shows that the scanning band is no longer in synchronism with the shaft whose speed it is sought to determine, the operator presses the trigger to release the indicator brake, adjusts the rheostat to bring the particular scanning band into synchronism with the shaft, 'presses the trigger to apply the indicator brake, reads the indicator, and makes a further check sight.v Y v `In order to make the indicating means easier to read. this means. is so constructed that the. nd-v Gator shaft |44 and. pointer |56 can rotate through four complete .revolutions when the scanning disc is broughtv up to maximum speed. Each revolution of the indicator shaft |44 moves the` auxiliary indicating shaft |82 through a quarter of av revolotion and causes a different number on the dial |92 to show through the window |94, and thereby indicate the number of complete revolutions of the pointer |56. In Fig. 6 thel pointer |56 and dial |92 are shown in the zero position. As the scanning disc shaft is brought up to one thousand R. P. M., the pointer |56 makes one complete rotation and the dial |92 moves so that number l appears through the opening |94. For example, if the scanning disc shaft had a speed of 1500 R. P. M., the pointer |56 would point at the number on the big dial |58, and the movable dial |92 would shift so that the gure 1 appears through the opening |94.

If the band of the scanning disc which is in synchronism with the shaft being measured has only a single clear segment or window, the shaft being measured would then have a speed of 1500 R. P. M. On the other` hand, if the band of the scanning disc which is in synchronism with the shaft being measured has a plurality of clear segments, the speed shown by the indicating mechanism must be multiplied by the number of clear segments of this particular scanning band. In this particularl application thel three scanning discs shown in Figs. i4, 1,5 andy 16V have bands` with clear segments varying in number from l to 16, so that with the highest band of the highest scanning disc it would be necessary to multiply theindicator showing by 16 in order to obtain the speed ofthe shaft or other part being measured.

On each scanning disc that band having the lowest number of windows is closest to the hub of the disc so that the' radial position of the particulai` scanning band being utilized will readily indicate the number of windows in this band provided that the operator knows which discr is in the machine. Special indicating means could readily be provided to indicate which of the three discs is. in` use, but such means would ordinarily constitute an unnecessary refinement since the operator can check his memory as to which disc is being used' by merely examining the two discs not in use.

While I have illustrated and described only two embodiments of my invention, numerous other variations and modifications may be made therein without departing from the scope ofmy invention, which includes all variations, modifications and equivalents coming within the appended claims.

I claim:

i. A portable. stroboscope of' thee-lass described, comprising a. pistol-like frame adapted to be d with its.` lengthwise axis; in substantial .t with an object to be viewed, a motor y said frame, a. drive shaft. driven by said motor, a scanning `disc mounted on said drive shaft transverselyV oi said axis, a governor for said drive shaft, means for varying the speed permitted by said governor, a rheostat for varying the speed; of; Said motor.. a common Control forl said rheostat and1 said governor varying means, anindicator r-indieating the. speed of said drive shaft,r said indicator being.v in a plane parallel with said dise, said frame having a part extending laterally` beyond said indicator, said being provided, with a` window aligned with part of said scanning disc` whereby said4 scan- 10 ning disc` may be viewed by sighting lengthwise of said frame, a brake for locking said indicator in speed indicating position, and a trigger for setting and releasing said indicator brake.

2. A portable stroboscope of the cla-ss described, comprising a pistol-like frame adapted to be pointed with its lengthwise axis in substantial alignment with an object to be viewed, a motor carried by said frame, a drive shaft driven by said motor, a scanning disc mounted on said drive shaft transversely of said aXis, a governor for saiddrive shaft, means for varying the speed permitted byv said governor, a rheostat for varying the speed of said motor, a common control for said rheostat and said governor varying means, an indicator for indicating the speed of said drive shaft, -said indicator being in a plane parallel with said disc, said frame having a part extending laterally beyond said indicator, said par-t being provided with a window aligned with a part of said scanning disc whereby said Scanning disc may be viewed by sighting lengthwise of said frame and a brake for locking said ndicator in speed indicating position.

3. A portable stroboscope of the class described, comprising a pistol-like frame adapted to be pointed with its lengthwise axis in substantial alignment with an object to be viewed, a motor carried by said frame, a drive shaft driven by said motor, a scanning disc mounted on said drive shaft transversely ofv said axis, a governor for'said drive shaft, means for varying the speed permitted by said governor, means for varying the speed of said motor,l a common control for said two last named means, an indicator forv indicating the speed of said drive shaft, said indicator being in a planeparallel with said disc, said frame having a part extending laterallyv beyond said indicator, said part being provided with a window aligned with a part of said scanning disc whereby said scanning disc may be viewed b-y sighting lengthwise of said frame, a brake for locking said indicator in speed indicating position, and means for setting and releasing said indicator brake.

4. A portable stroboscope of the class described, comprising a pistol-like frame adapted to be pointed with its lengthwise axis in substantial alignment with an object to be viewed, a motor carried by said frame, a drive shaftv driven by said motor, a scanning disc mounted on said drive shaft transversely of said axis, a governor for said drive shaft, an indicator for indicating the speed of said drive shaft, said indicator being in a plane parallel with said disc, said frame having a part extending laterally beyond said indicator, said part being provided with a window aligned with apart of said scanning disc whereby said scanning disc may be viewed by sighting lengthwise of said frame, a brake for locking; said indicator in' speed indicatingposition, and a` trigger for settingand releasing said indicator braker 5. A portable stroboscope of the class described, comprising a` frame having a longitudinal axis, a motor, a drive` shaft driven by said motor, a scanning disc mounted on said shaft transversely of said axis, a. rheostat for varying the speed of said motor, said rheostat including a. slider, a shaft for moving said slider, and a handle., for rotating said. shaft, a speed governor for said shaft comprising a collar attached to said shaft, a. second collar slidable axially of said shaft, and weight-s attached. tosaid. collars and eiectiveto vary the, position, of said sl'idable collar, anec.-

centric brake mounted on said rheostat shaft and engageable with said slidable collar to vary the speed control effected by said governor, said frame being pistol-like and supporting said motor, shaft, scanning disc and rheostat, and speed indicating means carried by said frame for indicating the speed of said drive shaft, said indicator being in a plane parallel with saiddisc, said frame having a part extending laterally beyond said indicator, said part being provided with a window aligned with a part of said scanning disc whereby said scanning disc may be viewed by sighting lengthwise of said frame, said scanning disc having a part laterally offset with respect to said indicating means.

6. A portable stroboscope of the class described, comprising a tubular housing, a motor carried by and within said housing, a drive shaft in axial alignment of the housing and driven by said motor, a scanning disc carried by said drive shaft, said disc being arranged transversely of said tubular housing, means for viewing an object through said scanning disc axially of the housing, a permanent electromagnet mounted on said drive shaft, a rst indicating shaft, a speed cup carried by said indicating shaft, a second indicating shaft geared to said rst indicating shaft, indicating means mounted on each of said indicating shafts, both indicating means being parallel to said scanning disc, a spiral spring having one end attached to said second indicating shaft and a second end fixed to said housing for urging said indicating shafts and speed cup to zero position, a brake drum mounted on said rst indicating shaft, a brake shoe engageable with said brake drum, a rst electromagnet for retracting said brake shoe, a latch to hold said brake shoe in retracted position, a spring for applying -said brake shoe, a second electromagnet for withdrawing said latch, a trigger movably mounted in said housing, a switch operating wheel driven by said trigger, a normally open electromagnet switch on each side of said wheel, projections extending alternately from opposite sides of said wheel for temporarily closing said switches, said projections and switches being so constructed and arranged that only one switch is closed for each actuation of said trigger, and an electrical connection between each switch and one of said electromagnets.

7. A portable stroboscope of the class described, comprising a housing, a motor carried by said housing, a drive shaft driven by said motor, a scanning disc carried by said drive shaft, a permanent electromagnet mounted on said drive shaft, an indicating shaft driven by said drive shaft, a brake drum mounted on said indicating shaft, a brake shoe engageable with said brake drum, a flexible arm supporting said brake shoe, a rst electromagnet for retracting said brake shoe, a latch engageable with said flexible arm to hold said brake shoe in retracted position, a spring for applying said brake shoe, a second electromagnet for withdrawing said latch, a pistol-like grip attached to said housing, a trigger movably mounted in said grip, a spring for urging said trigger in one direction, a switch operating wheel driven by said trigger, a normally open electromagnet switch on each side of said wheel, projections extending alternately from opposite sides of said wheel for temporarily closing said switches, said projection-s and switches being so constructed and arranged that only one switch is closed for each actuation of said trigger, and an electrical connection bel2 tween each switch and one of said electromagnets.

8. A portable stroboscope of the class described, comprising a housing, a motor carried by said housing, a drive shaft driven by said motor, a scanning disc carried by said drive shaft, a permanent electromagnet mounted on said drive shaft, a iirst indicating shaft, a speed cup carried by said indicating shaft, a second indicating shaft geared to said rst indicating shaft, indicating means operated by each of said indicating shafts, a spiral spring having one end attached to said second indicating shaft and a second end fixed to said housing for urging said indicating shafts and speed cup to zero position, a brake drum mounted on said first indicating shaft, a brake shoe engageable with said brake drum, a iiexible arm supporting said brake shoe, a rst electromagnet for retracting said brake shoe, a latch engageable with said flexible arm to hold said brake shoe in retracted position, a spring for applying said brake shoe, a second electromagnet for withdrawing said latch, a pistol-like grip attached to said housing, a trigger movably mounted in said grip, a pair of normally open electromagnetic switches operated alternately in response to successive actuations of said trigger to control said electromagnets, and means for causing said trigger to actuate said switches alternately.

9. A portable stroboscope of the class described. comprising a housing, a motor ca'rried by said housing, a drive shaft driven by said motor, a scanning disc carried by said driveshaft, a permanent magnet mounted on said drive shaft, indicating means driven from said shaft, a brake drum mounted on said indicating means, a brake shoe engageable with said brake drum, a flexible arm supporting said brake shoe, means for withdrawing said brake shoe, a, latch engageable with said iiexible arm to hold said'brake shoe in retracted position, a spring for applying said brake shoe, means for withdrawing said latch, a pistollike grip attached to said housing, a trigger movably mounted in said grip, a slidable actuator connected to said trigger, a spring for urging said actuator and trigger in one direction, a pawl carried by said actuator, a switch operating wheel driven by said pawl, a normally open electromagnet switch on each side of said Wheel, projections extending alternately from opposite sides of said wheel for temporarily closing said switches, said projections and switches being so constructed and arranged that only one switch is closed for each actuation of said trigger, and an electrical connection between each switch and one of said withdrawing means.

10. A portable stroboscope of the class described, comprising a housing, a motor carried by said housing, a drive shaft driven by said motor, a scanning disc carried by said drive shaft, a permanent magnet mounted on said drive shaft, an

indicating shaft, a speed cup carried by said indicating shaft, indicating means operated by said indicating shaft, a spiral spring having one end attached to said indicating shaft Iand a second end fixed to said housing for urging said indi eating shaft and speed cup to zero position, a brake drum mounted on said indicating shaft, a brake shoe engageable with said brake drum, a flexible arm supporting said brake shoe, a first electromagnet for retracting said brake shoe, a latch engageable with said flexible arm to hold said brake shoe in retracted position, a spring 'for applying said brake shoe, a second electromagnet for withdrawing said latch, a grip attached to said housing, a trigger movably mounted in said grip, a slidable actuator connected to said trigger, a spring for urging said actuator and trigger in one direction, a pawl carried by said actuator, a switch operating wheel driven by said pawl, a normally open electromagnet switch on each side of said wheel, projections extending alternately from opposite sides of said Wheel for temporarily closing said switches, said projections and switches being so constructed and arranged that only one switch is closed for each actuation of said trigger, and an electrical connection between each switch and one of said electromagnets.

11. A portable stroboscope of the class described, comprising a housing, a motor carried by said housing, a drive shaft driven by said motor, a scanning disc carried by said drive shaft, a permanent magnet mounted on said drive shaft, a first indicating shaft, a speed cup carried by said indicating shaft, a second indicating shaft geared to said rst indicating shaft, indicating means operated by each of said indicating shafts, a spiral spring having one end attached to said second indicating shaft and a second end fixed to said housing for urging said indicating shafts and speed cup to Zero position, a brake drum mounted on said first indicating shaft, a brake shoe engageable with said brake drum, a exible arm supporting said brake shoe, a first electromagnet for retracting said brake shoe, a latch engageable with said iiexible arm to hold said brake shoe in retracted position, a spring for applying said brake shoe, a second electromagnet for withdrawing said latch, a pistol-like grip attached to said housing, a trigger movably mounted in said grip, a slidable actuator connected to said trigger, a spring for urging said actuator and trigger in one direction, a pawl carried by said actuator, a switch operating wheel driven by said pawl, a normally open electromagnet switch on each side of said wheel, projections extending alternately from opposite sides of said wheel for temporarily closing said switches, said projections and switches being so constructed and arranged that only one switch is closed for each actuation of said trigger, and an electrical connection between each switch and one of said electromagnets.

FREDERICK Gr. SCHWEISTHAL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,930,460 Boulin Oct. 17, 1933 2,148,794 Ashdown Feb. 28, 1939 FOREIGN PATENTS Number Country Date 659,685 France Feb. 5, 1929 516,626 Great Britain Jan. 8, 1940 Certicate of Correction Patent No. 2,468,690. April 26, 1949. FREDERICK G. SCHWEISTHAL It is hereby certied that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 15, for the Word piston read pistol; and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 8th day of November, A. D. 1949.

[SEAL] THOMAS F. MURPHY,

Assistant 'ommz'ssioner of Patents. 

